Cone penetrometer technology (CPT) has been used widely for investigating strength properties in foundations and road subgrades for over 40 years, and for environmental purposes for the past five years. Prior art uses of cone penetrometer technology for environmental purposes have generally been limited to soil, soil gas, and ground water sampling.
Tensiometers are known in the art and are described, for example in the following U.S. patents which are incorporated herein by reference: U.S. Pat. No. 5,915,476 to Hubbell et al.; U.S. Pat. No. 5,758,538 to Hubbell et al.; and U.S. Pat. No. 5,644,947 to Hubbell et al. A conventional tensiometer includes a sealed tube defining a chamber which is normally completely filled with water, a hollow porous tip on one end of the tube, and a vacuum gauge connected to the water chamber. The porous tip is inserted in the soil and establishes liquid contact between the water in the tube and the moisture in the soil surrounding the tip. Relatively dry soil tends to pull water from the tube through the porous tip. However, because the tube is sealed, only a minute amount of water is actually withdrawn. Therefore, the water in the tube is placed under tension by the pulling effect of the dry soil, thus creating a measurable subatmospheric pressure in the tube. Higher moisture contents in the soil produce correspondingly less vacuum in the tube. Completely saturated soils register substantially zero vacuum or atmospheric pressure.
U.S. Pat. No. 5,915,476 to Hubbell and Sisson discloses an advanced tensiometer included in a monitoring well comprising a conduit defining a passageway, the conduit having a proximal end, an opposite distal end, and a given inside diametral dimension; a coupler connected in fluid flowing relationship with the passageway; a geophysical monitoring device dimensioned for slidable movement in the passageway which is defined by the conduit, and wherein the geophysical monitoring device has a connector for releasable mating cooperation with the coupler; and a porous housing borne by the coupler and connected in fluid flowing relation relative thereto.
Conventional techniques for installing tensiometers require drilling wells with hand augers (if shallow), hollow stem augers, or rotary drill rigs, resulting in drill cuttings being brought to the surface. The drill cuttings thus produced then have to be disposed.
Some monitoring sites have stringent requirements for drilling. In some sites, such as contaminated sites, it is undesirable to have drill cuttings removed to land surface or to have large diameter boreholes drilled. Therefore, it would be desirable to provide tensiometers that can be inserted into samples without the need for drilling.